On Wed, Jan 21, 2015, at 14:40, Denys Vlasenko wrote: > On Sun, Jan 18, 2015 at 12:45 PM, Alexander van Heukelum > <heuke...@fastmail.fm> wrote: > > The macro THREAD_INFO(reg,offset) is used in assembly to compute the > > offset between the user ptregs and the thread_info struct. Change > > the macro and all its uses so that offset is given as the current > > top of stack in the pt_regs frame. The generated code is identical. > > What is the purpose of doing this? > > I don't mean to say that it's pointless, but it is also not obvious > why it's better than the code before patch.
Just because I had a hard time understanding what the offset parameter means. Turns out Borislav did another variant in his patchset. Quoting him from the commit message which made that the change: > Semi-mysterious expressions THREAD_INFO(%rsp,RIP) - "why RIP??" > are now replaced by more logical THREAD_INFO(%rsp,SIZEOF_PTREGS) - > "rsp is SIZEOF_PTREGS bytes below the top, calculate > thread_info's address using that information" Borislav expresses "offset" as an offset from the stack's page boundary,while I chose the offset from the start of struct pt_regs on the stack. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
